1. Field of the Invention
The present invention relates to a printer with a paper aligning device for aligning a recording paper with a paper transport path in the printer.
2. Background Arts
As disclosed in Japanese Laid-open Patent Application No. 10-29356, a recording paper roll has been used in many kinds of printers. The recording paper roll is formed by winding a continuous web of recording paper around a cylindrical spool. The recording paper roll is held by a paper holder when it is set in a paper supply section of a printer, or in a paper magazine that is loaded in a magazine chamber of a printer. Then, the recording paper is fed out from the paper supply section or the paper magazine into a printing stage of the thermosensitive color printer. While the thermosensitive color printer is turned off or in a standby condition, the recording paper is rewound onto the roll, for protecting it from moisture.
As is well-known in the art, the recording paper supplied from the roll can be skewed relative to a paper transport path of the thermosensitive color printer, or a center line of the supplied recording paper can deviate from a center line of the paper transport path. If the recording paper is skewed or its center deviates, side edges of the recording paper may be bent or folded, or the recording paper may be jammed during the rewinding. To avoid such troubles, aligning devices for correcting the skewed or center-deviated recording paper have been developed.
An exemplary paper aligning device is disclosed in Japanese Laid-open Patent Application No. 8-143183, wherein a leading edge of the recording paper is pressed against a pair of feed rollers for correcting the skewed recording paper. At the same time, guide members are pressed onto opposite side edges of the recording paper for aligning the center of the recording paper with the center of the paper transport path.
Another type of paper aligning device is disclosed in Japanese Patent Publication No. 62-13248, wherein a stationary guide member is disposed on one lateral side of the paper transport path, and a movable guide member is disposed on the other lateral side of the paper transport path. The movable guide member is moved in a perpendicular direction to the transport path, to push one side edge of the conveyed recording paper such that the other side edge of the recording paper is pressed against the stationary guide member. Thereby the recording paper is aligned with the paper transport path.
In a printer using a recording paper roll, the aligning device is set at a retracted position away from the recording paper while a plurality of images are successively printed on the recording paper. This is for preventing damaging the side edges of the recording paper, especially for preventing damaging adhesive portions of such recording paper that is used for producing stickers. As a result, the recording paper tends to be skewed or deviated from the center during the successive printing.
Japanese Laid-open Patent Application No. 8-157120 discloses a teaching to apply a constant tension to the recording paper roll by a pair of paper holders that are attached to the opposite end faces of the recording paper roll. The tension improves stability in conveying the recording paper, so the recording paper is prevented from skewing or deviating from the center during successive printing. In this prior art, correction for the skewed or center-deviated recording paper is also executed immediately after the recording paper is set in the thermosensitive color printer, by making a plurality of times of precutting processes, whereby a leading end portion of the recording paper is cut off.
However, any of these conventional types of paper aligning devices involves a problem in that the recording paper sometimes cannot be aligned because it is resiliently bent by the pressure from the guide members. This problem is apt to occur in those printers which use different kinds of recording paper with different rigidity and stiffness, and those using such a recording paper roll that needs a large pressure for aligning. The conventional aligning devices also have a problem in that the recording paper is skewed again even after it is aligned, because of torsion of the recording paper that is provided between the recording paper roll and the aligning device by the aligning of the skewed paper itself.
Furthermore, since the recording paper is cut off the roll at the end of printing, if the cutting line is not rectangular to the side edges of the recording paper, the aligning device disclosed in Japanese Laid-open Patent Application No. 8-157120 cannot properly align the recording paper.
In the aligning device disclosed in Japanese Patent Publication No. 62-13248, because the movable guide member pushes the side edge of the skewed recording paper while maintaining the skewed condition, the other side edge of the recording paper comes to contact with the stationary guide member first at a point, so the side edge can sometimes be bent or folded at the contact point.
On the other hand, executing the precutting process a plurality of times, like in the prior art disclosed in Japanese Laid-open Patent Application No. 8-157120, elongates the total printing time and also consumes more recording paper.
An object of the present invention is to provide a printer with a paper aligning device that solves the above problems and aligns the recording paper with reliability.
According to the present invention, in a printer comprising a paper supply section for supplying a recording paper therefrom; a feed roller pair for nipping and conveying the recording paper along a paper transport path; a printing head for printing an image on the recording paper in synchronism with conveying movement of the recording paper; and an aligning device disposed in the paper transport path between the paper supply section and the printing head, for aligning the recording paper with the paper transport path, the aligning device comprises a pair of guide members placed so as to face side edges of the recording paper on the paper transport path so as to be able to pivot each on a perpendicular axis to a recording surface of the recording paper; a drive mechanism for shifting the guide members toward the side edges of the recording paper to push the side edges; and a stopping device for stopping the guide members at an aligning position as the guide members are shifted toward the side edges of the recording paper, wherein the recording paper is oriented parallel to the paper transport path as the side edges are confined by the guide members at the aligning position.
Since the guide members can pivot on the perpendicular axis to the recording surface of the recording paper, the guide members may be inclined relative to the parallel direction to the paper transport path, so the guide member may not push the side edge at a point even while the recording paper is skewed relative to the parallel direction to the paper transport path. Accordingly, the recording paper is prevented from being bent or folded by the guide members.
According to a preferred embodiment, the stopping device has a pair of stopping portions which the guide members come to contact with at the aligning position. By adjusting the position of the stopping portions in the lateral direction of the paper transport path and their angle relative to the parallel direction of the paper transport path, it is possible to determine the aligning position such that a center line of the recording paper is aligned with a center line of the paper transport path when the side edges are confined by the guide members at the aligning position.
By defining the distance between the stopping portions to be equal to a tolerable minimum width of the recording paper, the recording paper is aligned without fail even where there are variations in the width.
The paper transport path is preferably curved in a section passing through the aligning device. Thereby, the rigidity and stiffness of the recording paper is increased in the aligning device, reducing the risk of bending the recording paper by the pressure from the guide members.
It is preferable to provide a pair of position keeping rollers in the aligning device, so as to keep the recording paper in the aligned condition.
By applying tension to the recording paper appropriately in either conveying direction, the recording paper is prevented from being skewed or deviating from the center of the paper transport path, even while the recording paper is conveyed back and forth a number of times along the paper transport path.